The present invention relates to a method for controlling the speed of a vehicle, particularly under consideration of vehicles driving ahead.
From German Published Patent Application No. 42 42 700, it is known to mount a radar sensor or an infrared sensor on a vehicle to detect vehicles driving ahead. This radar sensor can be, for example, a module of a vehicle comfort and convenience system ACC (adaptive cruise control), in which information pertaining to the distance and the relative speed of the vehicle with respect to other vehicles and information on road conditions are continually processed.
The basic functions of the above described system are directed to controlling the vehicle speed, either to a setpoint value, here the desired speed, or to the speed of a vehicle driving ahead, in the case that the latter is traveling at a slower speed than the desired speed and is within the sensing range of the radar sensor. As mentioned above, this sensor can be, for example, a component of a microwave radar or of an infrared lidar and, to that end, it measures the distance, the relative speed, and the angle of objects, particularly of vehicles driving ahead within the sensing range.
From German Patent No. 197 22 947, a method is known, where, in addition to measuring the quantities described above, the future travel-course progression of the vehicle is included, along with the ACC system, in the control. For this, the future travel-course range of at least one vehicle driving ahead is determined, and a lateral offset is then ascertained for all detected vehicles. The future travel corridor to determine. Given steady-state curvature conditions of the roadway, i.e., in a linear portion or in the region of constant curvature of a curve, the future travel corridor is also able to be easily determined using the known method, with the aid of a well-adjusted yaw-rate or rotation-rate signal.
From the yaw rate of the ACC vehicle, the curvature of the roadway and, therefore, also the travel-course offset of a vehicle traveling ahead can be determined here, using generally known method steps. If this travel-course offset is smaller in terms of absolute value than a predefined width of the travel corridor, then one can infer that the vehicle traveling ahead is located in the travel corridor of the ACC vehicle. When working with changing conditions, particularly in the beginning curve region, however, one is normally no longer able to correctly determine the association with the travel corridor, so that it can happen that a vehicle driving ahead in the right, adjacent lane, near the beginning of a left curve, is incorrectly attributed to the travel corridor. This leads to faulty control reactions, the cause here being the mistaken curvature prediction, since the ascertained curvature is always specific to the current instant and, therefore, the reaction to a change in curvature is too late.
A method for controlling the speed of a vehicle of the type mentioned at the outset, where, in the vehicle to be controlled, the yaw rate or rotation rate is measured, in particular to determine the curvature of the vehicle""s own travel trajectory, and where, using a proximity sensor or position sensor, at least one vehicle traveling ahead or at least some other object within a sensor""s sensing range is detected with regard to an offset from the travel course of the vehicle to be controlled, is advantageously further refined in accordance with the present invention.
As already mentioned at the outset, curvature k of the roadway may be calculated in a simple manner from the measured yaw rate of the ACC vehicle to be controlled using generally known method steps in that the yaw rate is divided by the speed, and, using that, the travel-course offset yc of a vehicle traveling ahead may also be determined. Specifically, travel-course offset yc may by determined using the following formula:
xe2x80x83yc=yvxe2x88x92k*d2/2,
quantity yv being the measured lateral offset, without allowing for curvature k, and d being the distance between the vehicle to be controlled and the measured vehicle driving ahead.
If this travel-course offset yc is smaller in terms of absolute value than a predefined width ylane, then one may infer that the object or the vehicle is located in the travel corridor of the ACC vehicle, ylane corresponding approximately to one half of a lane width.
A collective shift in the radar targets may be utilized as an indication of a future change in the curvature. As long as the assumption can be made that vehicles driving ahead maintain their lane, their movement is already an early indication that a change in curvature follows. Thus, from the detection of a plurality of objects, the present invention provides for correcting the curvature of the vehicle""s own travel trajectory with a view to a prediction of an expected curvature, an averaging of positional changes ascertained at a plurality of the objects being taken as a basis here.
In an especially preferred specific embodiment, corrected curvature k is advantageously measured for the plurality of the detected objects in preset time intervals of angles xcex1i corresponding to lateral offset |yv|. For each object, angle variation dxcex1i from a measurement to the respective preceding measurement is determined, and, in each measuring cycle, angle variations dxcex1i are averaged over the collective detected objects, and divided by the time duration between the measuring cycles to generate a collective angular velocity xcex1Dtkoll. From the addition of collective angular velocity xcex1Dtkoll to the yaw rate measured in the vehicle to be controlled, a correction is then ascertained for a future curvature k of the travel trajectory of the vehicle to be controlled.
It is also advantageous when future curvature k is calculated by dividing the sum of the yaw rate and collective angular velocity xcex1Dtkoll by the driving speed of the vehicle to be controlled. Furthermore, angular variation dxcex1i, measured for each object, may be simply corrected in each instance by the relative velocity of the vehicle to be controlled in relation to the object""s movement and the yaw rate. To improve the measuring result, it is also possible, when ascertaining collective angular velocity xcex1Dtkoll over a plurality of measuring cycles, to average the values determined at any one time.
To obtain a still further improved method for predicting the travel-course progression of the vehicle to be controlled, it is also possible for a number of further detection devices for determining the travel-course offset of objects located ahead, to be present in the vehicle to be controlled. All results of these detection devices may then be analyzed and weighted. The analysis and weighting may preferably be carried out using a video camera, a preferably satellite-supported navigational system, or a set-up for determining a historical lateral offset of the vehicles driving ahead, or on the basis of a travel-course determination made by interpreting the position of fixed destinations determine the travel-course offset.